The present disclosure relates to a fan attachment structure provided for a blower unit of a vehicle air conditioner, for example.
Vehicle air conditioners are generally provided with a blower unit for supplying air-conditioning air to a heat exchanger (see, for example, Japanese Unexamined Patent Publication No. 11-343997). Such a blower unit includes a centrifugal fan, a fan housing to house the fan, and a motor to drive the fan. The motor has a metallic output shaft, which has a D-cross section by having its peripheral surface partially cut off. The fan is a resin molded product, and includes, at the center of rotation thereof, a cylindrical insert member to which the output shaft of the motor is fitted. The insert member is made of a resin material having higher mechanical strength than the resin material that forms the body of the fan.
A motor output shaft with a D-cross section such as the one disclosed in Japanese Unexamined Patent Publication No. 11-343997 certainly functions as an anti-slip in the rotational direction, but is difficult to balance its rotation by itself, which is not beneficial. In addition, the hardness of the metallic output shaft requires a non-negligible cost for partially cutting off the output shaft into a desired D-cross section.
To avoid these disadvantages, the motor may have a round bar output shaft with a circular cross section so as to have its rotation balanced easily and to be formed at a reduced machining cost. A round bar output shaft, however, is no longer engageable with the insert member in its rotational direction when fitted into the insert member, and will slip more easily in the rotational direction with respect to the insert member when rotating, thus possibly allowing relative rotations. The output shaft may be prevented from slipping if the entire fan is molded of a resin material with high mechanical strength with the insert member omitted, for example. However, this method results in an increased material cost and/or molding cost for the fan.
Another possibility may be more tightly fitting the output shaft into the insert member either by increasing the outer diameter of the output shaft or by decreasing the inner diameter of the insert member in which the output shaft is fitted. In that case, the round bar output shaft will generate a high stress substantially uniformly over the entire periphery of the insert member. In this structure, the insert member has been formed by molding a resin material, and therefore, has a weld line formed in a portion thereof where molten resin flows have merged with each other in the die during the molding process. A portion of the insert member with such a weld line is more vulnerable to the stress than the rest of the insert member. As described above, the stress is generated substantially uniformly over the entire periphery of the insert member by the output shaft fitted in. Thus, there is a concern about the insert member's cracking eventually, no matter where a weld line has been formed around the periphery.
It is therefore an object of the present disclosure to prevent a cylindrical anti-slip member of a resin material from cracking when a round bar motor output shaft is fitted into the anti-slip member.